Does anybody have any tips? Places to stop, eat, drink along the way? I would be in no rush and would likely take route taxi back to Negril as well.

Looks like this is the route?

Route Taxi Negril to Savanna- la-Mar.

At Savanna-la-Mar, there looks like two options to get to Treasure Beach.

Route Taxi to Whitehouse to Black River to Treasure Beach

or Mini Bus to Black River to Treasure Beach. .